DOUBLE PRECISION FUNCTION DSDOT(N,SX,INCX,SY,INCY) * .. Scalar Arguments .. INTEGER INCX,INCY,N * .. * .. Array Arguments .. REAL SX(*),SY(*) * .. * * AUTHORS * ======= * Lawson, C. L., (JPL), Hanson, R. J., (SNLA), * Kincaid, D. R., (U. of Texas), Krogh, F. T., (JPL) * * Purpose * ======= * Compute the inner product of two vectors with extended * precision accumulation and result. * * Returns D.P. dot product accumulated in D.P., for S.P. SX and SY * DSDOT = sum for I = 0 to N-1 of SX(LX+I*INCX) * SY(LY+I*INCY), * where LX = 1 if INCX .GE. 0, else LX = 1+(1-N)*INCX, and LY is * defined in a similar way using INCY. * * Arguments * ========= * * N (input) INTEGER * number of elements in input vector(s) * * SX (input) REAL array, dimension(N) * single precision vector with N elements * * INCX (input) INTEGER * storage spacing between elements of SX * * SY (input) REAL array, dimension(N) * single precision vector with N elements * * INCY (input) INTEGER * storage spacing between elements of SY * * DSDOT (output) DOUBLE PRECISION * DSDOT double precision dot product (zero if N.LE.0) * * REFERENCES * ========== * * C. L. Lawson, R. J. Hanson, D. R. Kincaid and F. T. * Krogh, Basic linear algebra subprograms for Fortran * usage, Algorithm No. 539, Transactions on Mathematical * Software 5, 3 (September 1979), pp. 308-323. * * REVISION HISTORY (YYMMDD) * ========================== * * 791001 DATE WRITTEN * 890831 Modified array declarations. (WRB) * 890831 REVISION DATE from Version 3.2 * 891214 Prologue converted to Version 4.0 format. (BAB) * 920310 Corrected definition of LX in DESCRIPTION. (WRB) * 920501 Reformatted the REFERENCES section. (WRB) * 070118 Reformat to LAPACK style (JL) * * ===================================================================== * * .. Local Scalars .. INTEGER I,KX,KY,NS * .. * .. Intrinsic Functions .. INTRINSIC DBLE * .. DSDOT = 0.0D0 IF (N.LE.0) RETURN IF (INCX.EQ.INCY .AND. INCX.GT.0) GO TO 20 * * Code for unequal or nonpositive increments. * KX = 1 KY = 1 IF (INCX.LT.0) KX = 1 + (1-N)*INCX IF (INCY.LT.0) KY = 1 + (1-N)*INCY DO 10 I = 1,N DSDOT = DSDOT + DBLE(SX(KX))*DBLE(SY(KY)) KX = KX + INCX KY = KY + INCY 10 CONTINUE RETURN * * Code for equal, positive, non-unit increments. * 20 NS = N*INCX DO 30 I = 1,NS,INCX DSDOT = DSDOT + DBLE(SX(I))*DBLE(SY(I)) 30 CONTINUE RETURN END